Our moon may be 100 million years younger than previously thought

An artist's rendering shows a planetary collision near the star Vega.… (NASA )

How old is the moon? Not as old as we once thought.

The moon is likely to be 4.4 billion to 4.45 billion years old, or about 100 million years younger than previously thought, according to new research by geochemist Richard Carlson of the Carnegie Institution of Washington.

It may be the closest body to us in space, but scientists are still not sure exactly how, or when, it formed.

The current working theory suggests that the moon formed when a large proto-planet plowed into the early Earth, creating a major explosion that sent huge amounts of rocky debris into space.

While most of that material returned to Earth, the theory suggests some of it stayed in space, forming a disk around the Earth that eventually grew together to form the moon.

While other scientists continue to improve their models of what this giant impact may have looked like, Carlson is trying to determine when it happened.

Like other scientists before him, he has been using radioactive dating to determine the age of lunar rocks collected during the Apollo missions.

Previous work in this area had a large margin of error, but Carlson says improved technology has allowed him to narrow that margin significantly.

"Back in the 1970s, you couldn't distinguish between 4.45 and 4.55 billion years," he told the Los Angeles Times. "Today, we can, and everything we are seeing suggests the 4.4 billion number."

One of the most interesting implications of Carlson's research is to imagine what the Earth might have been like before it had a moon.

"We know the age of the solar system very well -- 4.568 billion years," Carlson said. "So the Earth may have had two phases of its life -- one before the giant impact, and another one greatly modified by the impact."

Carlson presented his research this week at the "Origins of the Moon" meeting of the Royal Society.